Conventional vehicles used for commercial traffic, the transport of heavy loads and construction machinery, in some cases, comprise a speed regulation unit (cruise control). Such devices serve to control the speed to a desired value, but in the prior art, no device for desired speed control is known, which can be used by the vehicle in an overrun condition during overrun condition of the vehicle.
A braking system having a hydrodynamic retarder and a friction brake is known from DE 2923406 C2 and in the brake system, uses input magnitudes, a braking demand pressure and a pressure, which increases with the speed of the retarder. In a control unit, from these input magnitudes, an application pressure that acts upon the friction brake and an effective pressure in the retarder are produced as output magnitudes. In this case, the control unit modifies the effective pressure of the retarder proportionally to the pressure that varies with the speed of the retarder and, at the same time, limits it to a pressure that corresponds approximately to the braking demand pressure. The effective application pressure on the control element of the friction brake is set as the difference between the braking demand pressure and the effective retarder pressure.
The purpose of the present invention is to indicate a method for controlling the desired speed of a vehicle that comprises a retarder, during a condition of overrun, whose implementation during the overrun operation of the vehicle can set and maintain a desired speed.